Tholomura hexonia ( Haeckel, 1887 )

Zhang, Lanlan & Suzuki, Noritoshi, 2017, Taxonomy and species diversity of Holocene pylonioid radiolarians from surface sediments of the northeastern Indian Ocean, Palaeontologia Electronica (Cambridge, England: 2003) 7 (8), pp. 1-68 : 59

Tholomura hexonia ( Haeckel, 1887)

Figure 32.1-11

1887 Amphitholus (Amphitholura) panicium Haeckel , p. 668, pl. 10, fig. 4.

1887 Amphitholonium tricolonium Haeckel , p. 669, pl. 10, fig. 7.

*1887 Tholonium (Tholonilla) hexonium Haeckel , p. 679, pl. 10, fig. 17.

1887 Cubotholonium ellipsoides Haeckel , p. 682, pl. 10, fig. 15.

1992 Tholonium hexonium Haeckel ; Sugiyama, Nobuhara, and Inoue, pl. 11, fig. 9.

1995 Larcospira haliomma (Ehrenberg) ; van de Paverd, p. 190, pl. 53, fig. 8 (only).

1995 Spongurus minor (JØrgensen); van de Paverd, p. 151-152, pl. 53, fig. 11 (only).

1999 Cubotholus sp. Sharma, Singh, and Rawal, p. 262, pl. 2, figs. 30-31.

2003 Cubotholus sp. Sharma and Ram, pl. 3, fig. 9.

2005 Cubotholus sp. A . Zapata and Olivares, p. 86, fig. 4.2-3.

Description. Test consists of a spherical S1a, an ellipsoid 1st pseudo-concentric shell, and two levels of three sets of twin, flat, dome-shaped cupolas. No gates are present. The sutures between cupolas are shallow. A transverse section of the cupolas along a given plane shows an elliptical outline. Pores of the cupolas are polygonal to rounded polygonal with relatively fine pore frames. Polar radial beams extend along both sides of the Lt-axis from the S1a, but they do not pierce the outermost cupolas. No major radial spines are present.

Remarks. Haeckel (1887) divided Tholomura hexonia ( Haeckel, 1887) into five different “species” shown in the synonym list. These five “species” have common structures in the shapes and pore patterns of their cupolas, which suggests that they belong to the same species. “ Amphitholus panicum Haeckel, 1887 ” is a vertical view of this species with two pseudo-concentric shells, and “ Amphitholonium tricolonium Haeckel, 1887 ” is a Lt-view of this species with three pseudo-concentric shells. “ Tholonium hexonium ” and “ Cubotholonium ellipsoides ” are Pl-views of fully mature specimens. These “species” were simply named as specimens with a combination of different ontogenetic stages and orientations. Tholomura hexonia is similar to Tholomura polystyla ( Chen, 1987) in that these two species have clearly depressed sutures between cupolas. The fully mature specimen of T. hexonia is distinguishable from T. polystyla based on the absence of robust main spines, but this criterion is not useful for specimens of younger ontogenetic stages. In juvenile specimens, the former can be distinguished from the latter by its relatively flat cupolas compared to those of T. polystyla (the length ratio of cupola width to its height: 1.7–3.3 in T. hexonia and 1.2–1.9 in T. polystyla ). Because of differences in the size ratios between cupola width and height, the sutures between the cupolas are shallower in T. hexonia than in T. polystyla . The sizes of the equivalent pseudo-concentric shells also differ between these two species. This difference is difficult to apply practically for microscope identification of these two species, however.

Figures

FIGURE 32. Photographs of the encountered morphotypes of Tholomura. 1-11, Tholomura hexonia (Haeckel, 1887); 12-23, Tholomura pilula n. sp.; 24-32, Tholomura polystyla (Chen, 1987). 1-16, 19-23, 26-32, Pl-view at Type 1; 17- 18, 24-25, Lt-view at Type 1. Scale bar equals 0.1 mm. All specimens are from YDY05-01.